Stability and Control of the Twin Lift Helicopter System

As a step towards a better understanding of the dynamics of helicopter twin lift systems utilizing a spreader bar, (the configuration previously demonstrated by two CH-54's), a linear seven degree of freedom hover model was developed and a real-time interactive simulation study conducted. The inherent vertical stability provided by the spreader bar configuration, the effect of bar and cable geometry, and various control strategies for minimizing the pilot workload involved in maintaining separation were investigated. Pilot assessments of this single simulation has lead to the conclusion that manual control with a only conventional autopilot may be more feasible than originally thought, that vertical separation can be used safely to reduce horizontal separation, (and hence spreader bar weight), and that workload decreases as the payload is increased.